This invention relates to the testing of fiber optic cables, and more particularly to a method and apparatus for determining the packing fraction of such cable terminations.
As indicated in my prior U.S. Pat. No. 3,884,585 there is a requirement to determine the degradation of transmission of radiant energy through fiber optic cables. One reason for such losses is the breakage of the individual fibers that may occur during manufacture or installation and use. The above patented method is directed to assessing the amount of such breakage.
However, degradation of radiant energy transmission can also arise from other factors that are inherent in the manufacture of the terminated fiber optical cable, namely, the kind and thickness of the fiber cladding, and the amount of intersticial area between the fibers usually occupied by an epoxy or like material as determined by the quality of fiber packing during termination. The area of these non-energy transmitting areas obviously effects the total efficiency of the fiber optic cable in transmitting the energy.
The energy transmitting efficiency of the terminated fiber optic cable can be expressed in a term called packing fraction (P. F.), being defined as the ratio of the total sum of the cross-sectional areas of the various individual fiber filaments in the bundle, to the total area of the bundle. Thus, any transmission losses due to filament breakage would be included in the packing fraction.
To date, there are no known methods in the prior art for determining the packing fraction of a terminated fiber optic cable. The need for such a method arises when such an operational requirement is specified in U.S. Navy specification for the manufacture of such terminated cables for use in Navy systems.